An influential scientific panel on Thursday opened a new front in the campaign against the coronavirus, recommending booster shots of the Pfizer-BioNTech Covid vaccine for a wide range of Americans, including tens of millions of older people. But the experts declined to endorse additional doses for health care workers, teachers and others who might have higher exposure on the job.

The decisions were made by the C.D.C. panel, the Advisory Committee on Immunization Practices, in a series of votes, during which scientists agonized over their choices. The recommendations revealed deep divisions among federal regulators and outside advisers about how to contain the virus nearly two years into the pandemic.

Just a day earlier, the Food and Drug Administration authorized booster shots for certain frontline workers. But the C.D.C.’s advisers disagreed that the doses were needed by so many healthy people.

The next step is for Dr. Rochelle Walensky, the director of the C.D.C., to make a formal recommendation. If she follows the guidance of the agency’s advisory committee, as is typically the case, the agency’s guidance may conflict with that of the F.D.A.

One administration official said Xavier Becerra, the secretary of health and human services, might ultimately have to mediate between the two agencies.

“There’s a complexity here, because Dr. Walensky was part of the White House announcement” on boosters, said Dr. Ashish Jha, dean of the Brown University School of Global Health. “I think she’s going to feel some amount of pressure to authorize this for health care workers.”

Depending on what is decided, the White House is likely to begin promoting and rolling out a plan for booster shots as soon as Friday. That would be in keeping with the administration’s previously announced plan to offer the additional doses the week of Sept. 20.

Whatever the scientific reservations, millions are expected to seek out booster shots. In one recent poll, about three-quarters of vaccinated Americans said they would opt for a booster if the doses were available.

State health departments generally follow the recommendations of the C.D.C. But many Americans were scrambling for boosters even before the F.D.A.’s authorization, typically by finding a cooperative pharmacist or by claiming to be unvaccinated.

The C.D.C.’s advisers acted on what they described — with considerable frustration — as scant research, mulling over conflicting data points that seldom pointed in one direction.

In the end, the panel unanimously endorsed booster shots for adults over 65 and for residents of long-term care facilities, who most clearly will benefit.

The committee also backed the shots for people 50 to 64 with medical conditions that leave them at risk for severe Covid-19, as well as those 18 to 49 who have certain medical conditions, based on an assessment of their individual needs.